The goal of this proposal is to identify the signal transduction pathways and effectors required for adaptation in the innate immune response in the fly. We define adaptation here as an immune response that is stronger and more rapid during a second exposure than a first. Immunologists typically divide the immune system into two parts, innate and adaptive. By definition, the innate immune system is not considered to be adaptive. Our experiments have the potential to change the current innate immunity paradigm that defines innate immunity as being non-adaptive. We've found that the innate immune response of a fruit fly changes following an initial challenge and that the immune response retains a memory of this change for the life of the fly. This second immune response is specific and more protective than a naive immune response. Two different fly pathogens are able to elicit a primed response: Streptococcus pneumoniae, a Gram-positive bacterium and Beauveria bassiana, a fungus. If we genetically prevent the fly from making antimicrobial peptides (AMPs), we uncover a similar but cryptic response against E.coli. We refer to these protective effects as microbe-induced primed responses. These primed responses are specific: S. pneumoniae will not prime for B. bassiana or E.coli and vice versa. Our current hypothesis is that microbes induce priming due to the specific activation of hemocytes. Here we propose experiments to define the molecular pathways underlying this phenomenon in the fruit fly, which provides a simple and genetically tractable system. This proposal illuminates a hole in the current description of innate immunity that is most easily studied in the fly. By defining this biology in the fly, we can directly identify homologous pathways conserved in vertebrates. In general, a greater understanding of innate immunity should help us design new vaccine adjuvants and could provide us with methods of manipulating the innate immune system to increase its efficiency against pathogens or decrease its potential to cause pathogenesis. If we had methods of stably and specifically increasing the innate immune response in people we could develop new methods of blocking infections. Specific Aims: 1. Measure changes in hemocyte activity during the priming response and determine the contribution of antimicrobial peptide induction to priming. 2. Determine where and when candidate molecules are required for immunity against S. pneumoniae. (Toll signaling, JAK/STAT signaling and Dscam) 3. Identify transcriptional changes occurring during a priming response.